Bind view to Singleton attribute

Using Streamlit
,
1

Context

Hi,

I am trying to develop a graph viz with a Python backend. The graph in itself is rendered through html+js (using vis.js library). I simplified the issue I am having for the sake of clarity.

The architectural choice for my backend is to use singletons for some viz and result store components. I noticed something that I didn’t expect: Streamlit freezes (grey out, no view update) my components.html and it is actually true for any Python object impacted (i.e. imported/set) by the running script.

I am running this locally with Python 3.10.4, streamline 1.39.0

Minimal reproductible

File structure

$ tree .
  .
├── app.py
├── helper.py
└── metaclasses.py

Python

In app.py

import time

from metaclasses import ThreadSafeSingleton


class TestSingleton(metaclass=ThreadSafeSingleton):

    def __init__(self):
        self.count = 0

    @property
    def count_html(self):
        return f"<p> Count is {self.count} </p>"

    def incr(self):
        self.count += 1

    def incr_multiple(self):
        for _ in range(5):
            self.count += 1
            time.sleep(1)

In metaclasses.py

import threading
from typing import Any, Dict


class ThreadSafeSingleton(type):
    """
    Thread safe implementation of a singleton with a destroy method for reset
    """

    _instances = {}
    _singleton_locks: Dict[Any, threading.Lock] = {}

    def __call__(cls, *args, **kwargs):
        if cls not in cls._instances:
            if cls not in cls._singleton_locks:
                cls._singleton_locks[cls] = threading.Lock()
            with cls._singleton_locks[cls]:
                if cls not in cls._instances:
                    cls._instances[cls] = super(
                        ThreadSafeSingleton, cls
                    ).__call__(*args, **kwargs)
        return cls._instances[cls]

    @classmethod
    def destroy(mcs, cls):
        if cls not in cls._singleton_locks:
            cls._singleton_locks[cls] = threading.Lock()
        with cls._singleton_locks[cls]:
            if cls in mcs._instances:
                del mcs._instances[cls]

In app.py

# --- Testing ---
import streamlit as st
import streamlit.components.v1 as components
from testing import TestSingleton

# gets updated fine for incr as exec done when view should update
# however, doesn't update incrementally when incr_multiple
if st.button("Increment by one"):
    TestSingleton().incr()

if st.button("Increment mutiple"):
    TestSingleton().incr_multiple()
    
st.markdown("Count attribute: ")
st.write(TestSingleton().count)
st.markdown("Count HTML attribute: ")
components.html(TestSingleton().count_html)

Question

What can I do so that the streamlit views of the count and count_html properties incrementally update as the incr_multiple() updates them ?

Thank you very much for any time spent into this. It is very possible that I missed something in the documentation that could help so please let me know if you have ideas.

2

Fixed

Misregard of streamlit running on the MainThread by default. Works fine if your run the incr_multiple method in a separate thread (and change method architecture to not lock the Singleton).

3

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